A huge thanks to Burnham Beeches yesterday for hosting some of us for the day and showing us around the site. Below are some of the stand-outs from the day, which I am certain you will all appreciate!
The importance of functional units
As we can see in the below few images of a particularly striking beech pollard, very little of the structure of the tree needs to remain for the tree to persist as a living and functional organism. In this example, only one unit of vascularity supports a very small crown, though the beech is generally without significant fault. It could, potentially, persist in this state for many decades! Certainly, the two natural ‘props’ that support the crowd through a sort of tripod could, in their eventual failure, be the demise of this tree; assuming the functional unit cannot itself adequately support the crown. Depending on the rate of decay of this two ‘props’, this last vascular strip might (if decay is slow) – or might not (if the ‘props’ fail sporadically) – be able to lay down the necessary wood fibres for such mechanical support.
Reduction work on lapsed pollards
There comes a point where one has to make a decision – for what reason is a lapsed pollard being managed? If it is to be managed for the provision of habitat then the major failure of the structure might not be an adverse occurrence (to a degree!), though if the intent is to retain the pollards for as long a period as is at all feasible then it might be necessary to undertake quite extensive reduction work, in order to reduce the mechanical loading upon the old pollard head. As can be seen from the below beech, heavy reduction work has taken place and the crown architecture / good number of ripe buds that remain below the pruning points will hopefully ensure that this lower crown will function very effectively. Of course, where lapsed pollards don’t have this lower growth then a heavy reduction might not even be possible, though where such low growth exists then it does provide for more effective means of management, with regards to reduction work of the crown.
Submerged deadwood for reptiles
A terrapin uses a large section of a mostly-sunken stem for sunbathing, in the centre of a large pond. Indeed, this section of deadwood is an effective tool for the terrapin, which allows it to be exposed to direct sunlight and isolated from potentially aggressive mammals (that includes humans – seriously). Improving the texture and heterogeneity of this aquatic habitat with deadwood is evidently important, therefore!
As some of the old beech pollards are quite literally falling apart, safeguarding their structures against such cataclysmic failure is necessary, if their presence in the landscape is to be retained. For some, this involved reduction work, whilst for others it involves installing props to support either the enture tree or large / heavy parts of its structure. In the below two cases, we can see how props have been installed to stop the trees falling over completely.
As you’d very much expect from a place such as this, wood-decay fungi are found in relative abundance. Beneath, the best examples are shown – this includes less common fungi, which we also came across during the trip; or less common associations, as you’ll see for one particular set of photos!
Fomitopsis pinicola (red-banded polypore)
Along the stem of a beech, this single bracket of a very infrequently found (in the UK, anyway) wood-decay fungus, the red-banded polypore, resides. Adjacent to a colony of Bjerkandera adusta and above extensive swathes of Kretzschmaria deusta, exactly to what degree this fungus has secured the wood substrate is unknown, though the good thing is that it has produced a fruiting body and in sporulating!
Heterobasidion annosum (fomes root rot)
A common fungus but probably not one you see every day on hawthorn! Hidden beneath a branch ridden with Fuscoporia ferra (syn: Phellinus ferreus) and some leaves, a series of fruiting bodies were tucked away comfortably. Fungi love to throw curve-balls!
Ganoderma pfeifferi (bees-wax polypore)
Sadly, the host beech had recently failed, due to the decay caused by this fungus. With respect to the rot induced, the failure was seemingly a brittle one and thus the failure can be attributed to a significant loss of cellulose. The cross-section of the failed region also yielded some glorious ‘rosing’ patterns, which is something that has been seen in other cases of failure as caused by this particular fungus.
Fomes fomentarius (hoof fungus)
Found on both birch and oak, this species isn’t notably abundant in the south of England, where the pathogens Ganoderma australe / resinaceum / pfeifferi (in order of commonality) tend to be better suited. In the two instances shown below, fallen deadwood has provided the resource, which aligns with its colonisation strategy – that of awaiting stress / entire vascular dysfunction of an area or whole tree, before launching wide-scale colonisation activities.
Daedalea quercina (Oak mazegill)
Found quite frequently on dysfunctional wood of oak, this instance has provided the best sight yet of this species. As you can see, an oak monolith is utterly littered with fruiting bodies, which is genuinely a spectacular sight!
Single-celled organisms that may create larger structures as groups in order to reproduce, slime molds, whilst not considered active wood decayers, can be found colonising deadwood (Heilmann-Clausen, 2001). Deadwood of 10-22 years of age, Heilmann-Clausen (2001) alleges, is most optimal for slime molds – at least, for the species observed on the decaying beech logs that featured within the study. This correlates with current understanding of slime molds, which suggests species strongly prefer moist, well-decayed wood.
The presence of wood-decay fungi sporophores, or even simply mycelium within the wood substrate, may also act as a source of energy for slime molds (Ing, 1994). As mycelial networks and their associated sporophores may take some time to develop within deadwood, this may perhaps be a further reason for why slime molds are found in greater abundance on older woody debris. The presence of bacteria, also greater in abundance on older and heavily-decayed wood, may also influence slime mold presence, as bacteria can be utilised as a further source of energy (Heilmann-Clausen, 2001). Lodge (1997) describes some slime molds as “predators of decomposers”. Slime molds may also utilise decaying leaves as a habitat (Ko et al., 2009; Raper, 1941; Raper, 1951; Stephenson, 1989). Therefore, the decaying leaf litter-soil ‘zone’ is another potential niche for slime mold species (Landolt & Stephenson, 1986). Moreover, slime molds may be found upon the bark of living trees (Olive & Stoianovitch, 1973; Stephenson, 1989).
Away from wood, decaying leaves, and soil exclusively, the composition of a forest ecosystem may also have an impact upon slime mold density. Landolt et al. (2006) found that, whilst species diversity did not differ between deciduous-broadleaved and coniferous stands, the broadleaved sites were host to slime mold populations over four times more abundant than coniferous sites. The same study also identified that different species of slime mold would be found at different altitude levels within forests, and suggested different micro-habitats perhaps act as refugia for different slime mold species that may have once colonised greater ranges of forest.
Heilmann-Clausen, J. (2001) A gradient analysis of communities of macrofungi and slime moulds on decaying beech logs. Mycological Research. 105 (5). p575-596.
Ing, B. (1994) Tansley Review No. 62: The phytosociology of myxomycetes. New Phytologist. 126 (2). p175-201.
Ko, T., Stephenson, S., Jeewon, R., Lumyong, S., & Hyde, K. (2009) Molecular diversity of myxomycetes associated with decaying wood and forest floor leaf litter. Mycologia. 101 (5). p592-598.
Landolt, J. & Stephenson, S. (1986) Cellular slime molds in forest soils of southwestern Virginia. Mycologia. 78 (3). p500-502.
Landolt, J., Stephenson, S., & Cavender, J. (2006) Distribution and ecology of dictyostelid cellular slime molds in Great Smoky Mountains National Park. Mycologia. 98 (4). p541-549.
Lodge, D. (1997) Factors related to diversity of decomposer fungi in tropical forests. Biodiversity & Conservation. 6 (5). p681-688.
Olive, L. & Stoianovitch, C. (1974) A cellular slime mold with flagellate cells. Mycologia. 66 (4). p685-690.
Raper, K. (1941) Dictyostelium minutum, a second new species of slime mold from decaying forest leaves. Mycologia. 33 (6). p633-649.
Raper, K. (1951) Isolation, cultivation, and conservation of simple slime molds. The Quarterly Review of Biology. 26 (2). p169-190.
Stephenson, S. (1989) Distribution and ecology of myxomycetes in temperate forests. II. Patterns of occurrence on bark surface of living trees, leaf litter, and dung. Mycologia. 81 (4). p608-621.
No, this title is not a click-baiting one – it’s wholly serious!
Courtesy of some recent research undertaken by scientists on Deception Island, which is an actively volcanic island in the archipelago that forms the South Shetland Islands, we now have a fascinating glimpse of the fungal activity that can be found upon the abanonded 19th and early to middle 20th century timber-framed buildings found upon the island’s shores. Indeed, with 57% of the island being covered by glaciers, these buildings were built along the coastline and were used for research and European whaling purposes (Whalers Bay), up until the Chileans departed from Pendulum Cove in 1967. Nowadays, it’s a tourist area for those that quite fancy spending large sums exploring such a desolate island, as well as a research base for Spanish and Argentinian scientists.
As regards to prior research on the historic timber buildings upon the island, research has uncovered fungal decomposition of the timber by Ascomycete fungi, thereby inferring some timber has begun to degrade via a soft rot. However, brown and whit rot fungi had not previously been identified on the island to any marked degree (one fruiting Pholiota sp. sample was found on the wood of a buried whaling vessel in 1967), and thus this research sought to ascertain whether fungal diversity was more appreciable than previously understood. At this point, it is also worth noting that some Asocmycetous fungi are indigenous to the island (such as Cadophora spp.), being found as saprotrophs on the plants growing freely on the island. Moreover, the research enabled for an insightful look into fungal ecology in a location where soil temperature range from below freezing to as high as 90°C.
Using two sites on the island where such timber-framed buildings could be found, which were Whalers Bay and Pendulum Cove (see the below image for rather precise locations), very small wood fragments from the timber-framed buildings (largerly made of Pinus spp. and Picea spp. timbers, though also Betula spp.) were sampled (188 from Whalers Bay and 30 from Pendulum Cove) and taken back to the laboratory under sterile conditions for assessment in a growth medium comprised principally of malt extract agar. Following the placement of the samples within the agar for a few weeks and the subsequent transfer of growing mycelium into pure cultures, genetic analysis was undertaken to ascertain what fungi were present within the wood samples.
In total, 326 isolates were found from the total 218 sampled wood fragments. Indeed, as was probably expected, the large majority (79%) of the isolated were of Ascomycete fungi from 53 different taxa that were causing a soft rot. However, quite interestingly, 15% of samples (equating to 11 different taxa) were from the Basidiomycetes division and a few (6%) also belonged to the Zygomycota.
From the Basidiomycetes, which are probably more well-known to those who read this blog, 18% of isolates were from the genus Pholiota. Indeed, this genus is a frequently identified one in the UK and further afield, and the genetic analysis revealed that one particular clade of the genus was of the species Pholiota multicingulata, which was found exclusively at the Pendulum Cove site where the Chilean undertook their scientific research up until the late 1960s. Found across the South Pacific and notably in New Zealand, its presence in the Antarctic Peninsula is considered to be as a consequence of infected timbers brought over by the Chileans.
Other common wood-decay Basidiomycetes known to arboriculturists included Coprinellus micaceus and Coniophora puteana, though only one sample of each was identified from genetic analysis – both considered to have been introduced by the Europeans during whaling escapades. Postia pelliculosa, a brown rot fungus of gymnospermous wood, was also identified – as was Jaapia argillacea, which is a rare fungus within Europe and thus its finding at Whalers Bay presented the authors with some surprise.
With reference to the other fungal genera and species found, species from the genus Cadophora wthe most abundant and amounted to 20% of all identified fungal samples. Furthermore, Hypochniciellium species accounted for 13% of the total sample count and Phialocephala 7%. Pholiota, as a genus, contributed only to 4% of the total number of records. Importantly, it was also found that many of the historic timbers were extensively decayed by the same fungi at both sites, inferring potentially a long-standing decay arising from a fungal metapopulation on the island. Decayed timbers were found most observably around the locations where the timber was in contact with the soil, perhaps due to a higher moiture content within the wood facilitating for more effective hyphal ingression into the timbers and the localised warming of soils because of volcanic activity. At the Chilean base, white rots of the sampled timbers were found only just beneath the soil surface, with brown and soft rots being identified on timber from both sites in wood exposed to ambient conditions.
As alluded to within the preceding text, it is highly probable that the fungal isolates from the two sites were introduced alongside human migration to Deception Island. Certainly, there have been plenty of opportunities for spores to be deposited on the island, given the whaling and research activities over the past two centuries. Importantly, the current phenomenon of tourism to the island will facilitate potentially in the emergence of new fungal species, which makes future research prospects exciting as the inherent isolation of the site would have rendered it almost impossible for exotic fungi to have otherwise arrived on site and – assuming they had – there would have been no timber for them to colonise. In this respect, the research undertaken on this island outlines a very critical biosecurity risk: human migration.
A further aspect of interest from the results is that native Ascomycetous fungi to the island, which were found to be acting saprotrophically on native plants, broadened their host range to that of the exotic timbers introduced. Thus, the notion of fungal adaptation alongside a change in the potential inoculum base is given credence, which can again be related to current issues with fungal pathogens of trees within Europe and further afield.
I had the pleasure of attending the tree health event at Lesnes Abbey Wood, which sits within the outer skirts of London, on Thursday 9th March 2017. Hosted by the Forestry Commission, the purpose of the day was to provide the attendees with some information on the risks that the trees of London may soon be – or already are – subject to. In all, it was a very enjoyable day, and I share below the key findings from two of the earlier speakers.
Talk 1: The Tree Health Resilience Plan – a strategic approach to tree health
Presented by Andrea Deol, who works for DEFRA in their Tree Health Policy Team, this presentation discussed the approach currently being synthesised and undertaken by plant health authorities in Great Britain, with regards to safeguarding tree health against exotic pests.
Andrea first drew our attention to four recent reports released since 2013, with all pertain to tree health to some appreciable degree. Chronologically, these are:
From these reports, in addition to more recent and otherwise perhaps undocumented decisions made, DEFRA’s currently policy extends to 2020 – after which time, the policy will undoubtedly be extensively reviewed. This current policy has three principal arms, as regards to the means of safeguarding Great Britain against pests and diseases of trees. These three aspects of protection are pre-border, at the border and within mainland Great Britain.
Certainly, work before the border is very important, if we are to safeguard our shores from undesirable pests and diseases. For this reason, DEFRA take plant health screening very seriously and the Plant Health Risk Register is reviewed on a monthly basis by governmental ministers. Of course, for organisms that make their way to the border, it is then down to robust border checks to identify the organism, quarantine it and subsequently destroy it. If this fails, then DEFRA’s aim is to identify an outbreak and then reduce the impact of the outbreak by containing it swiftly and effectively. Identification measures principally arise through aerial and ground-based inspections, for which entire Forestry Commission teams also exist. Aerial inspection are, for example, utilised effectively as the means of identifying Phytopthora outbreaks in larch, where crown dieback is a main symptom of infection. For this reason, a formal contingency planning document was very recently released (in February 2017), which outlines how the government would respond to any outbreak event that impacts upon plants and trees in England – and bees. This document is entitled General Contingency Plan for Plant and Bee Health in England.
From this document, DEFRA’s objective is to be better protected against pathogenic organisms that impact upon plants and trees and possess a strong response and associated recovery capability to such potential outbreaks. Their associated vision is, with reference to trees, to build a treescape which is resilient and provides an array of valuable ecosystem services. Granted, such an objective and vision demands an intricate understanding of the threats facing Great Britain’s (specifically England) trees, a robust management team to manage outbreak events, otherwise healthy tree populations free of significant biotic and abiotic stress and also a good amount of species and genetic diversity. In this sense, monocultures are wholly bad and should be avoided, which includes along streets. In fact, clonally-propagated trees (such as London plane and fastigiated varieties of trees, which are so commonly found in urban environments) are a big no-no, as they are utterly diabolical in terms of their genetic diversity (or lack of!).
More on the topic of building a resilient treescape, an outline of what constitutes resilience was detailed. Specifically, this refers to a three-step process: recovery, adaptation and resistance. Beginning with recovery, this entails:
the formation of robust contingency plans should an organism arrive on these shores
the creation of solid re-planting programmes
the adoption and utilisation of good arboricultural and silvicultural practices
the responsible surveillance of at-risk areas
the synthesis of local, regional and national plans detailing all of the above
As for recovery, this involves:
the careful selection of trees being re-planted so that there is a solid diversity between and within the species (i.e. genetic diversity)
the sourcing of tree stock with provenance in mind, whereby local sources of seed are to be preferred over foreign imports
the increase of total tree cover within Great Britain, which sits at around 10% at present (of which 14% of trees are outside woodlands of over 2ha in size)
Lastly, adaptation demands:
the active diversification of tree populations
the design of planting schemes at the landscape-scale, which will demand many bodies liaise with one another over on choices and the location of such plantings
the effective management of deer populations
the allowance for trees to naturally reproduce via sexual means, so that resilience can emerge as a natural consequence of reproductive biology and not through clonal nursery propagation (which carries its own major risks)
Finally, it was stated that DEFRA is currently assessing its priorities, with regards to tree health. Indeed, a formal publication date of this plan is due to be some time during autumn of 2017, though there will be a public consultation prior to that document being formally published. Thus, it may be pertinent to monitor DEFRA’s activity, in anticipation of this draft report to be sent for consultation.
Presented by Keith Sacre of Barcham Trees PLC, the talk began by giving some context to the situation in Great Britain, with an obvious focus on London. This context was sobering, though the risks are very much real and thus must be treated with the respect they deserve.
For example, the potential emergence of the Asian longhorn beetle into London would cause untold damage to a potentially massive number of tree species. Because of its diverse host range and the warmer climate found within the urban zone (courtesy of the urban heat island effect), its virulence is perhaps more marked than if an outbreak occurred in a rural area (as it did in Kent during 2012, where sycamore – an ideal host tree – was the only significant host for the 563 beetles found in the outbreak). Therefore, when noting for London’s very diverse tree population, up to 31% of all of London’s trees could be impacted by this insect pest – a number that equates to 3,800,000 trees, which would have a replacement cost of a staggering £23,000,000,000.
Furthermore, ash dieback, which is presenting itself as a very widespread threat to ash in Great Britain, would – in London alone – kill a possible 374,195 ash trees. Not accounting for the ecosystem services ash provide and looking again solely at replacement costs, it is projected that it would cost £447,345,251 to replace the dead ash. As regards to plane wilt, which currently plagues parts of continental Europe, because London has a huge number of plane trees (9% of the total canopy cover in Inner London!) its emergence and impact would lead to 121,000 plane trees being felled / dying and an attributed replacement cost of £351,623,660.
Speaking more macrocosmically, Keith then alluded to whether it is wise to rely upon governmental institutions for tree health safeguarding. Indeed, as would be expected by such a rhetorical question, his answer was that it is probably not, for the response is generally too slow and reactive. Curiously, the working party for the British Standard 8545:2014 – Trees: from nursery to independence in the landscape – Recommendations, which relates to managing and planting nursery trees in the landscape, did try to put into the document a stipulation that any imported tree stock should always be quarantined before being dispatched to the buyer. However, and quite unfortunately – though not unexpectedly, due to current policy – the pursuit and sustenance of free trade trumps biosecurity, thereby meaning that the quarantine measure had to be revised significantly, else it would effectively be promoting something other than free trade.
On that note, Keith drew us back to the AA’s biosecurity policy, where he remarked that the fact that so many organisations from across the industry have endorsed the policy as being very positive, though did lament the lack of top-down communication from the board level to staff within such endorsing companies (as some individuals didn’t know their organisation had endorsed the document).
As an aside, an important piece of progress in biosecurity within Great Britain was the recent position change of the Royal Horticultural Society on tree imports for the Chelsea Flower Show. Importantly, they are now mandating all of the trees being imported are quarantined before being dispatched to the buyer for use at the show. Certainly, this is great news, though Keith did also detail the concerns that are so very evident regarding the lack of an integrated management plan that spans across land ownerships and incorporates different land owners. Specifically, he noted that whilst Royal Botanic Gardens Kew are managing their oak processionary moth issue effectively, a neighbouring landowner could do nothing whatsoever with their oak trees and thus put Kew at a yearly risk of reinfection. The means of solving such a problem were not addressed, though for the sake of limited time availability I can understand why.
Some say it’s written in the stars, though the only experience I have had with braille is from select old Nintendo games from the 1990s and early 2000s (revealing my age a little here!). Others say it’s just annoying. I’d probably agree with the latter! Regardless, here we have it: more pictures of fungi on trees.
As always, I keep my eye out for some interesting finds. This week has been pretty decent on the fungal side of things, though given the time of year only the perennial polypores are really observable – asides from the odd Flammulina velutipes / elastica and some enterprising Pleurotus species. Nonetheless, for the sake of showcasing unique finds and for educational purposes, here are a few species of polypore and some common agarics.
Firstly, we have a rather cool deck of Ganoderma resinaceum brackets around a rather pronounced buttress on an oak (Quercus robur). The fruiting between the two buttress roots is likely indicative of good reaction growth that is well-compartmentalised, which in turn infers respectable and probably sound (i.e. free of appreciable decay) buttressing from which the oak is supporting itself. We then have some shots of a rather aberrant duo of Trametes gibbosa on what is probably an old sycamore (Acer pseudoplatanus) stump, some Kretzschmaria deusta on (again!) sycamore, Ganoderma australe on a fallen ash (Fraxinus excelsior) and finally some Flammulina sp. and Pleutorus ostreatus on a very decayed stump of an unknown deciduous broadleaved species.
The arthropods are vast in terms of species, and include ants, beetles, butterflies, mites, moths, spiders, and so on. Therefore, covering the entire spectrum of arthropods in this section is impractical, though the general provisioning by trees will be outlined and species will be used to illustrate given examples.
Many arthropods are considered to be saproxylic in nature – they principally utilise dead woody material (both standing and fallen, in both dead and living trees) as habitat, for at least part of their life cycle, though they may also rely upon fungal sporophores associated with the presence of deadwood, as is to be detailed below (Gibb et al., 2006; Harding & Rose, 1986; Komonen et al., 2000). Of all the saproxylic arthropods, beetles are perhaps the most significant in terms of the proportion occupied of total saproxylic species worldwide (Müller et al., 2010), though saproxylic flies also feature in great numerical abundance (Falk, 2014; Harding & Rose, 1986).
Beetles may be either generalist or specialist in nature (on either broadleaved or coniferous hosts), and they will normally require a host with an abundance of deadwood (or large sections of coarse woody debris) usually over 7.5cm in diameter that resides within an area typically not heavily shaded (Müller et al., 2010; Siitonen & Ranius, 2015). This may be, in part, due to many beetle species (in their adult stage) requiring nectar from herbaceous plants, which would be lacking in woodland with significant canopy closure (Falk, 2014; Siitonen & Ranius, 2015). This means that veteran trees amongst wood pasture and parklands (including in urban areas) may be particularly suitable (Bergmeier & Roellig, 2014; Harding & Rose, 1986; Ramírez-Hernández et al., 2014; Jonsell, 2012; Jørgensen & Quelch, 2014), though this is not at all a steadfast rule as species may also be found abundantly in (perhaps more open) woodland, and particularly where there are large amounts of veteran trees and deadwood – around 60 cubic metres per hectare, according to Müller et al. (2010). Granted, they are found particularly in older (mature to veteran) trees, including within cavities that possess wood mould, water-filled rot holes, dead bark, exposed wood, sap flows, fruiting bodies (of fungi and slime moulds), mycelia of fungi, dead branches, and dead roots (Carpaneto et al., 2010; Falk, 2014; Harding & Rose, 1986; Siitonen & Ranius, 2015; Stokland et al., 2012). Beetle species may also not necessarily associate preferentially with a species (or group of species), but with the conditions aforementioned that are present within a tree (Harding & Rose, 1986; Jonsell, 2012). At times, preferable conditions may be an infrequent as one veteran tree in every hundred (Harding & Rose, 1986).
Despite this, species preference is observed. For broadleaved obligates, heavier shade may be more necessary, and in such instances there is a closer affinity of the beetles with fungal mycelium. Because fungi tend to produce more mycelium in cooler and more humid conditions (though this does, of course, vary with the species), the broadleaved obligates may therefore be found normally in greater abundance where conditions are more suited to fungal growth, and their presence may thus be associated with a canopy openness of as little as 20% (Bässler et al., 2010; Müller et al., 2010). This is, of course, not a steadfast rule, and many open wood pastures may support a great abundance of saproxylic beetles (Harding & Rose, 1986).
It is also important to recognise that many species of saproxylic beetle are reliant upon particular stages of the wood decay process. For instance, species that require fresh phloem tissue will only be able to colonise briefly in the first few summers following on from the death of the phloem tissue (Falk, 2014). Other species require significantly-decayed wood in a particular micro-climate, and even of a particular tree species (Harding & Rose, 1986). There also exist intricate associations between species of fungi and saproxylic insects. Inonotus hispidus, which is usually found upon ash, is the habitat for Triplax russica and Orchesia micans, whilst the coal fungus (Daldinia concentrica), also oft found upon the deadwood of ash (Fraxinus excelsior), is the main provider of habitat for Platyrhinus resinosus (Falk, 2014). The birch polypore (Fomitopsis betulina) is also host to numerous species of Coleoptera (Harding & Rose, 1986); as is the polypore Fomitopsis pinicola (Jonsson & Nordlander, 2006; Komonen, 2003; Komonen et al., 2000). This means that these species may be found where there is a suitable population of the fungus’ host species, where sporophores are present and will likely fruit again in the future, across numerous trees, and for many years. Most beetle species rely on oak more so than other tree species however, as oak generally lives for much longer and thus provides a wider array of different micro-habitats, and possesses increased compositional complexity as a result (Harding & Rose, 1986; Siitonen & Ranius, 2015).
Therefore, the loss of suitable habitat through active management programmes (including logging, and felling trees for safety reasons in urban areas) will have a very adverse impact upon saproxylic beetles, though also certain species of moth, and even species associated with saproxylic insects, including parasitic wasps, solitary wasps (which use beetle bore holes for habitat), and predatory Coleoptera (Harding & Rose, 1986; Komonen et al., 2000). Curiously, research by Carpaneto et al. (2010) concluded that trees that were ranked as the most evidently ‘hazardous’ were host to the most saproxylic beetle species, and their removal would therefore have a drastic impact upon local populations. Similarly, fragmentation of woodland patches suitable for saproxylic populations has led to a decline in the meta-populations (Grove, 2002; Komonen et al., 2000), as has deadwood removal in a managed site itself (Gibb et al., 2006). Interestingly, though not surprisingly, ‘deadwood fragmentation’ also has an adverse impact upon saproxylic insect populations (Schiegg, 2000).
Both ants and termites also benefit from the presence of deadwood. With regards to both, nests will usually form at the base of a tree or at an area where there is at least moderate decay – enough to support a viable population (Jones et al., 2003; Shigo, 1986; Stokland et al., 2012). Ants and termites both follow CODIT (compartmentalisation of damage in trees) patterns in relation to how their nests progress, and thus their territory will increase as fungal decay propagates further into the host. Ants will not feed on the decaying wood of the host however, and will simply use the decaying site as a nesting area. Conversely, termites will feast upon decayed wood and essentially control (perhaps by slowing down) the spread of fungal decay in a manner that provides as much longevity of the host as possible for a viable nesting site (Shigo, 1986). In tropical rainforests, termites are in fact considered to be one of the principal means of wood decomposition (Mori et al., 2014), and thus the provisioning of deadwood habitat is absolutely critical. Without decaying wood within trees therefore, ants and particularly termites will lack a potential habitat, and thus where a stand is actively managed populations may be markedly reduced (Donovan et al., 2007; Eggleton et al., 1995). Of course, termites are not necessarily to be desired when they are invading the wood structure of a property, and therefore deadwood is not universally beneficial (Esenther & Beal, 1979; Morales-Ramos & Rojas, 2001) – at least, when human properties are involved.
The presence of deadwood may also be beneficial for ground-nesting and leaf-litter dwelling spiders, which can utilise downed woody debris (particularly pieces with only slight decay) for both nesting and foraging (Varady-Szabo & Buddle, 2006). In fact, research by Buddle (2001) suggested that such spiders may more routinely utilise downed woody material when compared to elevated woody material (dead branches and telephone poles) because of the greater array of associated micro-habitats, and particularly at certain life stages – such as during egg-laying, for females (Koch et al., 2010). Furthermore, as fallen woody debris can help to retain leaf litter (or even facilitate in the build-up leaf litter), spider populations are more abundant and more diverse in sites where such woody debris is present (Castro & Wise, 2010). Therefore, where woodlands are managed and areas are clear-cut, spider populations may be markedly reduced in terms of the diversity of species. However, generalist species may benefit from the amount of cut stumps (Pearce et al., 2004). Curiously, Koch et al. (2010) suggest that spiders may perhaps benefit from woodland clearance, because the vigorous re-growth of trees and the higher light availability to the woodland floor (promoting herbaceous plant growth) increases the abundance of potential prey. Despite this, old-growth species will suffer (Buddle & Shorthouse, 2008), and thus the population structure of spider populations may dramatically change.
Soil mites are a further group that benefit from coarse woody debris, though also from hollows and holes throughout the basal region of a tree (including water-filled cavities), and from fungal sporophores and hyphae associated with wood decay (Fashing, 1998; Johnston & Crossley, 1993). Typically, termites will use fungi and insects found within the wood as a food source, and the wood structure itself will provide for an array of niche micro-habitats that are critical at different life stages of a mite. Certain mite species are obligates that associate with coarse woody debris exclusively, and may in fact only be associated with certain species’ woody debris. Additionally, mites may utilise woody debris and hollows within trees to parasitise upon other species using the ‘resource’, with both lizards and snakes being parasitised by mites following their frequenting of such resources. Beetles may also be parasitised, though the mite in such an instance may use the beetle as a means of entry into woody debris (Norton, 1980).
It is not just deadwood that arthropods will utilise, however. Foliage, both alive and abscised, is also of use (Falk, 2014). For example, the ermine moth (Yponomeutidae) will rely upon the living foliage of a host tree as a food source, and the bird cherry ermine moth (Yponomeuta evonymella) is one example of this. During late spring, larvae will fully defoliate their host Prunus padus, before pupating, emerging, and then laying eggs upon the shoots ready for the following year (Leather & Bland, 1999). Many other moth species will, during their larval stage, also behave in such a manner and thus defoliate their host – either entirely, or in part (Herrick & Gansner, 1987). Other species may alternatively have larvae mine into the leaf and feed upon the tissues within (Thalmann et al., 2003), such as horse chestnut leaf miner (Cameraria ohridella). Flies, including the holly leaf-miner (Phytomyza ilicis), will also mine leaves in a similar fashion (Owen, 1978). Ultimately however, the same purpose is served – the insect uses the living tissues of a leaf to complete its life cycle, and fuel further generations.
Fallen leaf litter, as briefly touched upon earlier when discussing spiders, may also be of marked benefit to many arthropods. Ants, beetles, and spiders are but three examples of groups that will utilise leaf litter as a means of habitat (Apigian et al., 2006). Beetles will, for instance, rely upon leaf litter to attract potential prey, though also to provide niche micro-climates that remain relatively stable in terms of humidity, light availability, and temperature (Haila & Niemelä, 1999). Their abundance may, according to Molnár et al., (2001) be greatest at forest edges, perhaps because prey is most abundant at these edge sites (Magura, 2002). Of course, this does not mean that edges created through artificial means will necessarily improve beetle populations, as research has shown that there are few ‘edge specialists’ and therefore populations usually will go into decline where there has been significant disturbance. Unless management mimics natural mortality events of forest trees, then constituent beetle populations may thus suffer adversely (Niemelä et al., 2007).
With regards to ants, Belshaw & Bolton (1993) suggest that management practices may not necessarily impact upon ant populations, though if there is a decline in leaf litter cover then ants associated with leaf litter presence may go into – perhaps only temporary (until leaf litter accumulations once again reach desirable levels) – decline (Woodcock et al., 2011). For example, logging within a stand may reduce leaf litter abundance for some years (Vasconcelos et al., 2000), as may (to a much lesser extent) controlled burning (Apigian et al., 2006; Vasconcelos et al., 2009), though in time (up to 10 years) leaf litter may once again reach a depth suitable to support a wide variety of ant species. However, the conversion of forest stands into plantations may be one driver behind more permanently falling ant populations (Fayle et al., 2010), as may habitat fragmentation (Carvalho & Vasconcelos, 1999) – particularly when forest patches are fragmented by vast monoculture plantations of tree or crop (Brühl et al., 2003). The conversion of Iberian wood pastures to eucalyptus plantations is one real world example of such a practice (Bergmeier & Roellig, 2014).
Also of benefit to many arthropods are nectar and pollen. Bees, beetles, butterflies, and hoverflies will, for instance, use nectar from flowers as a food source (Dick et al., 2003; Kay et al., 1984), and generally (but not always) a nectar source will lack significant specificity in terms of the insect species attracted (Karban, 2015). Despite this, different chemicals secreted by different flowers, and the toxicity of certain nectar sources to particular insects, means certain tree species may only be visited by certain insect species (Adler, 2000; Rasmont et al., 2005). Tree diversity may therefore be key to sustaining healthy insect populations (Holl, 1995), and where species may prefer to frequent herbaceous plant species the presence of a diverse woodland canopy above may still be very influential (Kitahara et al., 2008). This may be because a diverse array of woody plant species increases the diversity of herbaceous species. At times, pollen may also be a reward, as may (more rarely) a flower’s scent. Karban (2015) remarks that all are collectively dubbed as ‘floral rewards’.
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